The present invention relates to power transfer apparatus and methods, and more particularly, to apparatus and methods for transferring power to a load from multiple alternative sources.
Computers, computer networks, telecommunications networks, medical equipment and other infrastructure often utilize redundant power sources to ensure that services and data are maintained in the event of loss or degradation of a primary power source, such as an AC utility line. For example, computers and network devices often are powered by uninterruptible power supplies (UPSs) that can maintain an AC supply from an alternative source, such as a battery-powered inverter.
In many applications, multiple sources of AC power may be available. For example, a load may be served from either a "preferred" source, such as an AC utility line, or from a less preferred secondary source, such as a motor-generator set. These multiple AC power sources may be supplied to a transfer switch that selectively connects the multiple AC power sources to a common AC power bus connected to the load. The transfer switch may operate automatically responsive to voltage or other conditions associated with the multiple AC power sources and/or the load. An example of such a transfer switch apparatus is described in U.S. Pat. No. 6,137,706 to Nesbitt et al.